Department of Chemistry & Biochemistry, Miami University, Oxford, OH 45056, USA.
Biomolecules. 2019 Nov 5;9(11):705. doi: 10.3390/biom9110705.
Polyphenols such as epigallocatechin gallate (EGCg) may have roles in preventing some chronic diseases when they are ingested as components of plant-based foods and beverages. Human serum albumin (HSA) is a multi-domain protein that binds various ligands and aids in their transport, distribution, and metabolism in the circulatory system. In the present study, the HSA-EGCg interaction in the absence or presence of fatty acid has been investigated. Förster resonance energy transfer (FRET) was used to determine inter- and intra-domain distances in the protein with and without EGCg and palmitic acid (PA). By labeling Cys-34 with 7-(diethyl amino)-4-methylcoumarin 3-maleimide (CPM), the distance between Trp-214 at domain IIA and CPM-Cys-34 at domain IA could be established. A small amount of PA decreased the distance, while a large amount increased the distance up to 5.4 Å. EGCg increased the inter-domain distance in HSA and HSA-PA up to 2.8 and 7.6 Å, respectively. We concluded that PA affects protein conformation more significantly compared to EGCg. Circular dichroism (CD) established that EGCg affects protein secondary structure more significantly than PA. PA had little effect on the α-helix content of HSA, while EGCg decreased the α-helix content in a dose-dependent fashion. Moreover, EGCg decreased α-helix content in HSA and HSA-PA to the same level. Dynamic light scattering (DLS) data revealed that both PA and EGCg increased HSA aggregation. EGCg increased HSA aggregation more significantly and promoted formation of aggregates that were more heterogenous. Any of these effects could impact the ability of serum albumin to transport and stabilize ligands including EGCg and other polyphenols.
多酚类物质，如表没食子儿茶素没食子酸酯（EGCg），当它们作为植物性食物和饮料的成分被摄入时，可能在预防某些慢性疾病方面发挥作用。人血清白蛋白（HSA）是一种多功能蛋白质，可结合多种配体，并有助于它们在循环系统中的运输、分布和代谢。在本研究中，研究了脂肪酸存在或不存在时 HSA-EGCg 的相互作用。利用荧光共振能量转移（FRET）测定了有无 EGCg 和棕榈酸（PA）时蛋白质的分子内和分子间距离。通过用 7-（二乙氨基）-4-甲基香豆素 3-马来酰亚胺（CPM）标记 Cys-34，建立了位于 IIA 结构域的色氨酸（Trp）214 和位于 IA 结构域的 CPM-Cys-34 之间的距离。少量的 PA 降低了距离，而大量的 PA 则将距离增加到 5.4 Å。EGCg 分别使 HSA 和 HSA-PA 的分子间距离增加了 2.8 和 7.6 Å。我们得出结论，与 EGCg 相比，PA 更能影响蛋白质构象。圆二色性（CD）表明，EGCg 比 PA 更能显著影响蛋白质二级结构。PA 对 HSA 的α-螺旋含量几乎没有影响，而 EGCg 则以剂量依赖的方式降低α-螺旋含量。此外，EGCg 降低了 HSA 和 HSA-PA 中的α-螺旋含量至相同水平。动态光散射（DLS）数据表明，PA 和 EGCg 均增加了 HSA 的聚集。EGCg 更显著地增加了 HSA 的聚集，并促进了聚集物的形成，这些聚集物的异质性更大。这些影响中的任何一种都可能影响血清白蛋白运输和稳定配体（包括 EGCg 和其他多酚类物质）的能力。
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